Potential overflows stemming from severe weather events are increasing along with the required public notification efforts. These types of overflow events do not just cause bad press and media attention, but can also result in a $1 per gallon fine and a required $2 per gallon fee to address the issue going forward.
To minimize the risk of these sanitary sewer overflows (SSOs) and their consequences, SSO abatement programs have evolved into a hybrid “find and fix” initiative that significantly decreased wet weather flows, minimized the potential for SSOs, increased collection system reliability, and decreased public health risks and environmental pollution.
The City of Largo, Florida experienced recurring SSOs during periods of heavy rainfall and undertook a $38-million wet weather program to address their pump station and force main capacity problems. However, wanting to alleviate the SSO problem altogether, the City implemented an inflow and infiltration (I&I) reduction program in the affected areas.
Largo’s approach to SSO abatement was founded on the projected effects of I&I source remediation, using hydraulic capacity analysis as the primary driver. The new program streamlined the manner in which necessary data sets were collected, analyzed and developed. The approach included completion of comprehensive sewer system evaluation survey (SSES) activities and hydraulic capacity analysis. The SSES tasks identified both stormwater-related inflow and excessive groundwater infiltration sources through smoke/dye testing, manhole inspections, night flow isolations and CCTV inspections. The hydraulic modeling initiative was completed using flow/rainfall/groundwater data captured over an 8-month period.
The results of a subsequent data assessment were merged with the modeling outcome to identify which pipes were at capacity under average flow vs wet weather flows. Once the capacity achievement analysis was completed, a prioritized infrastructure renewal and replacement program was created and the improvements completed utilizing in-place “on-call” construction contracts.
Click here or on the image above to review the presentation by McKim & Creed and the City of Largo at the 2019 Southwest Florida Water and Wastewater Expo. If you would like more information, contact Kris Samples, PE at firstname.lastname@example.org.